Hello all, I had this error when installing as well.
I did manage to finally restart my computer in 10.12 Sierra, as opposed to installing 10.13, and wanted to let others know about it, as this page was one of the top results as I was trying to desperately find a way to either install or recover. I'll get 10.13 installed soon, but I was a bad user and didn't back up before trying to install the first time. I will do that now.
In the meantime, for those that haven't had success installing 10.13, and are in this same could not install loop, and simply would like to get back to 10.12, here is what I did: Once I received the "could not be installed on your computer message" and it told me to quit the installer and restart, I went to Apple logo in the upper left (maybe had to click a bit to make the menu bar appear?), and there was an option to choose the startup disk. It had my 10.12.6 system folder as an option, I chose it, it restarted, and instead of booting with the Installer, it booted normally! I'm backing up now and very happy I didn't screw myself over.
Mildly interestingly, I have a Bootcamp partition, and in troubleshooting, I wanted to be sure the partition was fine, so I booted using Option to choose a drive to start up from. In this view, the two partitions were disk images. I point this out to contrast it to when I chose the start up disk from the menu bar option, the images were the OS folders and names, not the disk image icons and names. Hope this ramble may offer an additional person another avenue of success.
